In the art of hydraulics, it is often necessary to reduce the pressure of a fluid, such as steam or oil, from a high value, which may exist in a source of supply, to a lower value, for use in a load device. One common type of restrictor for this purpose is simply a single sharp edged orifice. Such a restrictor reduces the pressure, but does so by generating very high fluid velocities. These high velocities in turn cause rapid erosion of the orifice edges and, what is even more important in some cases, causes intolerable high noise levels.
Another kind of restrictor comprises many long, narrow passageways such as a number of small tubes bound together or a number of long holes drilled in a block of metal. Such restrictors have been used successfully but, among other disadvantages, they are expensive to manufacture.
Another kind of restrictor is the simple tortuous path restrictor in which the fluid is forced to flow through one or more sinuous paths thereby generating friction which reduces the pressure. One disadvantage of such a restrictor is that the reduction in pressure varies greatly with the viscosity of the fluid.
Another kind of restrictor which has been known in the past is the matrix restrictor in which the fluid is passed through a porous matrix, thereby reducing pressure by friction. One difficulty with such a restrictor is that the extremely small passages required tend to become plugged due to the contamination inherent in any working fluid. If larger passages are used, the restrictor becomes very bulky.